THE gas disasters at Lake Nyos in 1986 （1 746 casualties） and Lake Monoun in 1984 （37 casualties）,both in Cameroon, were caused by a sudden release of a large amount of CO<sub>2</sub> stored in these l...THE gas disasters at Lake Nyos in 1986 （1 746 casualties） and Lake Monoun in 1984 （37 casualties）,both in Cameroon, were caused by a sudden release of a large amount of CO<sub>2</sub> stored in these lakes. TheCO<sub>2</sub> is derived from a magmatic source, judging from the isotopic ratio of δ<sup>13</sup>C=-3.5±0.2‰ （PDB）and that of helium associated with the CO<sub>2</sub>, i.e. <sup>3</sup>He/<sup>4</sup>He-8×10<sup>-6</sup> or 5.7 R<sub>a</sub> where R<sub>a</sub> is the <sup>3</sup>He/He ratio of the atmospheric helium. Follow-up surveys of Lake Nyos （209 m deep） revealed that thetemperature, concentration of dissolved ionic species （TDS） and free-CO<sub>2</sub> generally co-vary and their profiles show a large decrease in the surface layer, limited change at mid depths and a significant increasetowards the lake bottom. This simultaneous increase in temperature, conductivity and free-CO<sub>2</sub> in the bottom water supports the view that CO<sub>2</sub> is being supplied to the lake in the form of warm, CO<sub>2</sub>-charged,mineralized water. Our recent observations （1993-1996） indicate that Lake Nyos still contains 12.4 gi-展开更多
文摘THE gas disasters at Lake Nyos in 1986 （1 746 casualties） and Lake Monoun in 1984 （37 casualties）,both in Cameroon, were caused by a sudden release of a large amount of CO<sub>2</sub> stored in these lakes. TheCO<sub>2</sub> is derived from a magmatic source, judging from the isotopic ratio of δ<sup>13</sup>C=-3.5±0.2‰ （PDB）and that of helium associated with the CO<sub>2</sub>, i.e. <sup>3</sup>He/<sup>4</sup>He-8×10<sup>-6</sup> or 5.7 R<sub>a</sub> where R<sub>a</sub> is the <sup>3</sup>He/He ratio of the atmospheric helium. Follow-up surveys of Lake Nyos （209 m deep） revealed that thetemperature, concentration of dissolved ionic species （TDS） and free-CO<sub>2</sub> generally co-vary and their profiles show a large decrease in the surface layer, limited change at mid depths and a significant increasetowards the lake bottom. This simultaneous increase in temperature, conductivity and free-CO<sub>2</sub> in the bottom water supports the view that CO<sub>2</sub> is being supplied to the lake in the form of warm, CO<sub>2</sub>-charged,mineralized water. Our recent observations （1993-1996） indicate that Lake Nyos still contains 12.4 gi-
